Deserialize OffsetDateTime from serde_json::Value

[madmaxio]

Hi, I'm using this simple code

use time::OffsetDateTime;

fn main() {
    let now = time::OffsetDateTime::now_utc();
    let ser = serde_json::json!(now);

    println!("{:?}", ser);
    
    let de = serde_json::from_value::<OffsetDateTime>(ser);

    println!("{:?}", de);
}

and getting error:

String("2021-11-22 21:34:12.1901555 +00:00:00")

Err(Error("invalid type: string \"2021-11-22 21:34:12.1901555 +00:00:00\", expected a borrowed string", line: 0, column: 0))

Any hints how to fix it?

[jhpratt]

Please provide some more context. What version of time are you using? What features are enabled? Without basic info there's not much I can do.

[mihai-dinculescu]

I'm getting the same error with the following dependencies

serde_json = "1.0.71"
time = { version = "0.3.5", features = ["serde-human-readable"] }

[madmaxio]

My dependencies are same:

time = { version = ""0.3.5", features = ["serde-human-readable"] }
serde_json = "1.0.71"

[jhpratt]

Thanks. I'll look into this when I get a chance.

[madmaxio]

Perhaps any ideas for workaround? I'm using Value enum pretty heavy and need this to work.

[jhpratt]

Using threads is helpful for organization.

There is no update. I've been busy, especially with Thanksgiving. If you put together a PR I will review it when possible.

[madmaxio]

Well, I checked the place in code where deserialize is called, but no idea how to fix.

[jhpratt]

After investigation, this is a limitation of serde_json. That crate needs to provide a way to get a &str when deserializing, which is something serde supports.

While time could theoretically support this by deserializing an owned String, I will not be doing this. Not only is it needlessly inefficient (allocating when not necessary), but it is a forward compatibility concern in that I wouldn't be able to support no-alloc human-readable parsing in the future without it being a breaking change. As such I suggest you create a feature request on the relevant repository.

[jonasbb]

This is a bug in this crate not in serde_json. Requesting a borrowed str while only needing a transient str (https://serde.rs/lifetimes.html#transient-borrowed-and-owned-data) is unfortunately a common problem. This breaks deserialization whenever an escape sequence is used or when the input cannot be borrowed from, e.g., for Value like types and deserialization from Read.

[jhpratt]

I didn't say it was a bug in serde, I said it was a limitation of serde_json. Those are two very different things. Per the link that you provided, all that's needed is transient data. If you're aware of a way to do this with serde_json::Value, please submit a pull request.

By the way, 👎 on a response just because you disagree with it is in no way how you're going to convince me to look further into something. My time is valuable and I am providing this for free. This is a complex project and one use case failing is not a priority. No one, yourself included, has provided any information on how to solve the problem that is claimed to exist. That's fine, but don't be rude while doing so.

[jonasbb]

It is not a limitation of serde_json. I look into providing a PR later. The 👎 is mainly because your answer is factually wrong. All you need to get a transient string is a small Visitor like https://github.com/jonasbb/serde_with/blob/c427b8e32177b4547eb3b4a90647dd438a390335/serde_with/src/rust.rs#L82-L110
It also has the benefit of providing a better error message with expecting.
The information how to do this is in the link I provided above. I didn't mean to come across rude.

[jhpratt]

I've never used a custom visitor before, so I didn't think it'd be necessary to create one. It still seems like serde_json could (and imo should) provide a cleaner way to do this. Regardless I'll check this out once I finish some other work.